In recent years, a remote-control system has being widely used to control locking/unlocking vehicle doors from a distance by communicating between a mobile device and an antenna device installed in the vehicle.
The conventional antenna device for use in such a remote-control system is described with reference to FIG. 6. FIG. 6 shows a cross-sectional view of conventional antenna device 10. Substantially box-like case 1 formed from a non-conducting material has opening 1A in the top surface, and extended terminals 2A and 2B are embedded in the left hand side of case 1 as shown in FIG. 6. Extended terminals 2A and 2B are molded integrally with case 1.
Case 1 includes antenna part 3. Antenna part 3 includes: ferrite core 3A; coil 3B wound on the outer periphery of ferrite core 3A; and capacitor 3C connected in series with coil 3B. The winding start of coil 3B is connected to extended terminal 2A and the winding end of coil 3B is connected to an end of capacitor 3C. The other end of capacitor 3C is connected to extended terminal 2B.
Extended terminals 2A and 2B are respectively connected to lead wire 5 outside case 1. The joints of extended terminals 2A and 2B to lead wire 5 are respectively covered by heat shrinkable tube 9 to prevent external exposure and the other end of lead wire 5 is connected to an in-vehicle unit (not shown) installed in a vehicle via a junction connector (not shown).
Antenna part 3 is sealed into case 1 using filler 6 such as silicon resin or epoxy resin. Filler 6 filled into case 1 is cured at a predetermined temperature to secure antenna part 3 inside case 1.
Lid 4 has locking holes 4A on both sides. Hooks 1B engage with locking holes 4A to cover opening 1A of case 1 by lid 4.
The operation of antenna device 10 is described next.
Antenna device 10 with above configuration is installed for instance inside a vehicle door handle. When a user who has a mobile device approaches the vehicle, the mobile device receives signal waves from antenna device 10. The mobile device decodes the signal waves received and transmittes a responding signal to antenna device 10. The in-vehicle unit installed in the vehicle decodes the responding signal received by antenna device 10 and controls locking/unlocking of the vehicle doors. The user can thus control locking/unlocking the vehicle doors by only carrying the mobile devic.
For example, Japanese Patent Unexamined Application No. 2001-345615 discloses such a conventional art.
However, since the conventional antenna device 10 is housed inside a door handle or the like and is therefore apt to getting wet by raindrops or water drops in vehicle washing, the waterproofing is necessary for antenna part 3 in antenna device 10. After antenna part 3 is housed, therefore, case 1 is filled with filler 6 and is then cured to secure antenna part 3 inside case 1.
However, merely filling and curing filler 6 is not sufficient to obtain good water proofing performance. Filler 6 must be kept under an atmosphere of reduced pressure such as vacuum or the like to release air trapped in filler 6 during the filling process before filler 6 is cured so as not to form residual bubbles. As described above, conventional antenna device 10 needs a long time and complicated processes for production.